1. Field of the Invention
The present invention relates to a vapor phase epitaxial growth apparatus for epitaxially growing silicon (Si) on a semiconductor substrate.
2. Description of the Prior Art
By the conventional silicon epitaxial growth method, a single crystalline lowly-doped semiconductor layer can be formed on a single crystalline highly-doped semiconductor layer. Alternatively, a single crystalline semiconductor layer can be selectively formed only at an opening portion of a semiconductor substrate (this is referred to as selective epitaxial growth method). This method can form semiconductor constructions which are difficult to accomplish by other methods. In addition, by the epitaxial growth method, since high-quality single crystalline layer free of defects can be obtained, this method can be applied to the production of various semiconductor devices such as bipolar LSI devices and part of MOS LSI devices.
As examples of vapor phase growth apparatuses for use in the Si epitaxial growth method, a Barrel Type shown in FIG. 7 and a Pancake Type shown in FIG. 8 are well known.
In FIG. 7, reference numeral 1 represents a reactive gas inlet tube. A heating lamp 3 is disposed around a quartz reaction tube 2. In the quartz reaction tube 2, a susceptor 4 for disposing semiconductor substrates 5 is provided. The susceptor 4 is rotated by a rotating shaft 6.
In FIG. 8, the same parts as those in FIG. 7 have the same reference numerals. The semiconductor substrates 5 are disposed on the susceptor 4. The semiconductor substrates 5 are heated from the lower portion of the susceptor 4 by use of RF current on working coil 9.
In FIGS. 7 and 8, a reaction gas received from the reaction gas inlet tube 1 causes a crystalize layer to grow on the layers of the semiconductor substrates 5. The resultant reaction gas is exhausted from an exhaust tube 7.
However, since such an apparatus can process only a small number of semiconductor substrates in a particular unit time, improvement of the process capacity of semiconductor wafers per unit time performance has been required. As the diameter of wafers increases, the number of wafers which can be processed in the unit time decreases. Thus, a countermeasure for decreasing the process cost has been desired.
According to such requirements, a vertical hot wall type vapor phase growth apparatus which laminately stacks wafers has gained popularity. FIG. 9 is a plan view of the vertical hot wall type vapor phase growth apparatus of a related art. The same parts as those in FIGS. 7, 8 and 9 have the same reference numerals.
In the vapor phase growth apparatus shown in FIG. 9, a reaction gas inlet tube 1 for introducing a reaction gas is disposed inside an inner tube 12 and in parallel with a side portion of a boat 13. The reaction gas inlet tube 1 is short in length and is disposed in the vicinity of a bottom portion of the boat 13. The reaction gas is sent upwardly from a top portion of the reaction gas inlet tube 1 and exhausted from an exhaust opening 17 at the top portion of the inner tube 13.
When the above-mentioned vertical hot wall type vapor phase growth apparatuses are used, the process capacity can be improved around 10 times higher than those of conventional apparatuses. Although these apparatuses have a problem of non uniformity of film thickness, by using a dual reaction tube or a nozzle for the reaction gas inlet tube 1, the flow of the reaction gas can be suitably controlled.
However, when the epitaxial growth of Si is conducted with the conventional vertical hot wall type vapor phase growth apparatuses, there is a problem of wall deposition where Si is deposited on a side wall of the dual reaction tube 19.
Wall deposition tends to take place uniformly on the inner surface of the inner tube 12 because the reaction gas tends to flow uniformly in the vicinity of the inner tube 12. This wall deposition can contribute to uniformity of the temperature distribution in the inner tube 12 because the heat from the heater 10 is mainly conducted by radiation. In other words, to prevent the temperature uniformity degradation of the inner tube 12, Si may be actively deposited on the inner wall of the inner tube 12.
On the other hand, wall deposition does not take place uniformly on the outer surface of the inner tube 12 and the inner surface of the outer tube 11 because the reaction gas does not flow uniformly between the inner tube 12 and the outer tube 11. Thus, the wall deposition of Si which takes place on the surfaces of quartz glass of the inner tube 12 and the outer tube 11 sometimes causes part of quartz glass to become opaque or grow a crack. Consequently, the wall surface of the dual reaction tube 19 becomes breakable, whereby a safety problem arises. In addition, since the temperature distribution in the dual reaction tube 19 becomes nonuniform, dust is easily generated.